Beer’s foam does not have specific criteria. The foam quantity depends on many factors such as : particular capacitance which is filled, of the intense of loading, the degree of churning and also from the temperature. So the foam sises might be much different.
According to foam quality is possible to accurately to determine the quality of the beer.
Roughly speaking, the beer foam should have following properties: density, durability and a profusion.
After the beer has been poured into the glass, foam should stay 4-5 minutes and the range adjustment being at least 4 cm. The foam of beer with low quality would be lower than a standard and will disappear very quick. So, the taste of this beer will be not the best.
To estimate a quality of beer foam and the beer, it is enough to pour beer into a glass and to blow on it. If the foam starts to disappear it means pour-quality beer. At the same good beer foam will deform as you like, and just not disappear.
There is one more way to assess the quality of the foam is its stickiness. In this case you would need to pour it out or to drink it. As a result, on the walls of the glass will have to be foam traces. If you see such you may be sure that you drink a good quality product!